Filter two lists that have same elements to only obtain a list with distinct elements using Java Stream

Question

I have list1 and list2 like below

List<String> list1 = List.of("DX4555", "DY4897", "FG4333", "IH09992");
List<String> list2 = List.of("DX4555", "DY4897", "FG4333", "IH09992", "LJ48833", "YTR3888");

What I would like to achieve is to have a list that only contains elements in list2 that are not in list1 which are unique which are ["LJ48833","YTR3888"]

I would like to achieve this using Java Stream

I have tried using stream().distinct(), but it's not working.

Answer 1

Stream.distinct() only allows you to discard elements that are present multiple times in the same collection or as they are iterated.

I suggest using ListUtils.subtract from apache commons, but you can also do it with streams, like this:

List<String> result = list2.stream()
.filter(item -> !list1.contains(item))
.collect(Collectors.toList());

Notice that it's an O(n^2) algorithm, due to the fact that List.contains is linear. If your lists are big, you should replace them with sets to be more efficient.